Project Summary Through NIDCD funding (R21DC013172) we showed that noise-induced temporary damage to the auditory dendrites is more severe when the exposure occurs at night compared to the day. Preliminary data strongly suggest that circulating glucocorticoids, which peak at nighttime in mice, are responsible for the greater sensitivity to night noise trauma. In absence of circulating glucocorticoids (by adrenalectomy), mice exposed to night noise show complete recovery of their auditory brainstem thresholds, and have their synaptic ribbons protected. RNAseq data show that inflammatory pathways rise at nighttime in the cochlea, and this is abolished in adrenalectomised mice, suggesting that inflammatory response could underlie the greater vulnerability of the auditory synapse. The RNAseq identified 7211 genes in the cochlea that have circadian expression and 65% of these genes show maximal expression at night-time. Since it is not standard practice in the auditory field to collect samples at different time points throughout the day a full understanding of gene regulation during the day and the night in the cochlea is lacking. Our laboratory is currently addressing this challenge with the following aims: Specific Aim 1: To identify glucocorticoid-dependent inflammatory signals that display circadian patterns and are triggered by day or night noise trauma in the cochlea. Hypothesis: GCs modulate inflammatory signals in a circadian manner causing a greater inflammatory response to night noise trauma compared to the day. Specific Aim 2: To determine whether Bmal1 in the cochlea regulates the GC-dependent inflammatory signals in response to day or night noise trauma. Hypothesis: In the cochlea, the core clock protein Bmal1 regulates the circadian cytokine release in response to noise and causing synaptopathy. Specific Aim 3: To develop new pharmacological treatments targeting the circadian machinery to protect from inflammatory-triggered noise-induced synaptopathy. Hypothesis: Inhibition of the clock at nighttime can prevent night noise-induced synaptopathy via the inhibition of inflammatory responses. This project will clarify how circadian and glucocorticoid-dependent inflammatory signals cause cochlear synaptopathy after temporary noise trauma. A battery of functional methods (auditory electrophysiology, noise trauma), quantitative morphological methods (cochleograms, spiral ganglion neuron counts, pre/post synaptic counts) and molecular methods (genetic mouse models, RNA seq) will be used. Ultimately, novel drugs that will modulate circadian rhythms could emerge to prevent and treat from noise-induced synaptopathy. Our results will introduce a new concept to the auditory field, namely, chronopharmacology, where optimal efficacy of drug treatment depends on the time of administration. The novel theoretical concept of this proposal is that the optimal function of the auditory system requires periods of activity followed by rest that is tightly regulated by clock genes. As simple and obvious as this may sound, this concept has neither been previously explored in the context of noise trauma nor treatment strategies.